Coating agent pump

ABSTRACT

The disclosure relates to a coating agent pump for conveying a coating agent in a coating installation, in particular for conveying paint in a painting installation, with an electric drive motor for driving the coating agent pump so that the coating agent pump continuously changes its pump position during operation. The disclosure provides a position measuring system for quantitatively detecting the pump position of the coating agent pump.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage of, and claims priority to, Patent Cooperation Treaty Application No. PCT/EP2017/060456, filed on May 3, 2017, which application claims priority to German Application No. DE 10 2016 005 945.1, filed on May 17, 2016, which applications are hereby incorporated herein by reference in their entireties.

The disclosure relates to a coating agent pump for conveying a coating agent in a coating installation, in particular for conveying paint or high-viscosity materials in a painting installation.

BACKGROUND

In modern painting installations for painting components (e.g. motor-vehicle body components), as a rule piston pumps are used for conveying the paint to be applied, these being driven pneumatically or being electrically powered, an electrically-powered double-piston pump for conveying paint being known for example from U.S. Pat. No. 7,938,632 B2. In this case, usually asynchronous motors are used as the drive motor.

The known paint pumps, however, have various disadvantages.

For example, the piston pumps operated by compressed air which were briefly mentioned first hereinbefore have a high energy consumption, this being associated with correspondingly high operating costs.

With electrically-powered piston pumps with asynchronous motors as drive motors as well, the energy consumption is relatively high: this applies in particular in the lower speed range. Furthermore, the speeds of asynchronous motors can only be limitedly low, since otherwise overheating due to high starting currents occurs.

Furthermore, the conveyed stream of paint in piston pumps of this type exhibits relatively high pulsation, since the pulsation of the conveyed stream of paint is determined by the quality of the mechanical deflection system or by the speed of reversal of the drive motor.

Furthermore, with the known electrically-powered piston pumps, further measuring and safety devices are necessary in order to avoid excess-pressure situations. To this end, as a rule a pressure sensor and/or an overpressure switch have to be arranged downstream from the piston pump.

One further disadvantage of the known piston pumps is that in order to keep the paint pressure in the line system constant further measuring devices (e.g. pressure sensors), with the aid of which a control loop can be established, are necessary.

Furthermore, it should be mentioned that as a rule only piston pumps with a small displaced volume are suitable for use as a metering pump, whereas piston pumps with a large displaced volume do not have the necessary dispensing accuracy.

Finally, it would be desirable to recognise a pump defect, which may for example be due to wear, in piston pumps of this type in good time.

With regard to the prior art, reference should also be made to DE 602 10 287 T2, DE 41 30 295 A1, U.S. Pat. No. 7,938,632 B2 and WO 2008/138848 A2.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a coating installation according to the disclosure,

FIG. 2 is a perspective view of the coating agent pump of FIG. 1,

FIG. 3 is a cut-open perspective view of the upper part of the coating agent pump of FIGS. 2, and

FIG. 4 is a cross-sectional view of the lower part of the coating agent pump of FIG. 2.

DETAILED DESCRIPTION

The coating agent pump according to the disclosure includes first of all, in line with the prior art, an electric drive motor for driving the coating agent pump. It should be mentioned here that the coating agent pump continuously changes its pump position during operation. In a technical implementation as a piston pump, this means that the piston position of the piston pump changes continuously during operation, since the piston or pistons oscillate(s) back and forth.

The coating agent pump according to the disclosure is distinguished by a position measuring system and optionally a torque or force measuring system which makes it possible to detect the current pump position of the coating agent pump quantitatively and associate it with a force on the piston or a torque on the shaft. In the case of a piston pump, therefore, the piston position(s) is/are detected by the position measuring system.

In this case it should be mentioned that there is a difference between the quantitative determination according to the disclosure of the pump position on one hand and the known qualitative determination of the pump position on the other hand. Thus it is known for example from the prior art, in the case of a piston pump, to detect the end stop points of the piston stroke by magnetically activated reed switches. In this case, however, it is ascertained only qualitatively whether the end stop points of the piston stroke are reached or not.

The quantitative detection according to the disclosure of the pump position offers various advantages, which will be discussed in detail later.

For example, the position measuring system may be integrated in the coating agent pump. To this end, the electric drive motor may for example be designed as a servomotor, which has as a component of the position measuring system an integrated position sensor in order to ascertain the position of the drive motor and hence also the pump position. There is however alternatively also the possibility of a separate rotary encoder being provided, which is connected to the drive motor and thus detects the angular position of the drive shaft and thus also the pump position.

Alternatively, there is however also the possibility of the position measuring system being structurally separated from the coating agent pump.

Furthermore, it should be mentioned that the position measuring system may ascertains an absolute value of the pump position, in contrast to an incremental value of the pump position.

Such a position measuring system with an absolute value as output signal can be capable of associating all the positions of the deflection system between the drive motor and piston within one revolution with the corresponding revolution of the drive motor, or of measuring the position of the slides, which are connected to the piston, on the rails. The initial association may take place either by a corresponding stipulation by the user via an input system or, as in the case of the use of incremental position measuring systems, via what are called “teach-in runs”. In such case, paint is conveyed at a low and constant speed (for safety reasons) over a few revolutions. In this case, pressure fluctuations occur on the line at the reversal points of the pistons, as a result of which the forces acting on the pistons also change. This change in forces is propagated via the deflection system to the shaft of the drive motor. The change in force is measured by the position measuring system (force measuring system or torque measuring system). Thus association of a path point with the point of the pulsation, and hence with the reversal point of the piston, is made possible. If the reversal point is known, then in turn all the further positions of the deflection system and hence also of the piston are known, since the relationship of angle of the deflection system and position of the position measuring system is determined during the design stage. The torque can in this case be determined either via a current measurement within the drive motor or via torque shafts on the shaft of the drive motor or via strain gauges. Alternatively, a force measurement can take place by strain gauges on the piston or pistons.

In this case it should be mentioned that the torque/force measuring system is not inevitably connected to the position measuring system. An encoder serves e.g. for measuring the position; the current detection on the other hand serves for calculating the torque.

There is however alternatively also the possibility of the position measuring system merely ascertaining an incremental value of the pump position or of the angular position of the drive shaft of the drive motor.

In one example of embodiment of the disclosure, the drive motor is a synchronous motor. It should however be mentioned that the disclosure can in principle also be implemented with other types of electric motors, so the extent of protection is not limited to a coating agent pump with a synchronous motor as drive motor.

It has already been mentioned above that the position measuring system quantitatively detects the pump position of the coating agent pump. To this end, the disclosure takes into account the technical-physical finding that the mechanical loading of the drive motor fluctuates correspondingly cyclically during a pump cycle. Thus, for example, in the case of a piston pump pressure fluctuations occur at the reversal points (dead centres) of the pistons, which fluctuations are associated with a corresponding fluctuation of the mechanical loading of the drive motor. The reversal points of the piston can therefore be recognised by monitoring the mechanical loading of the drive motor. In one example of embodiment of the disclosure, the position measuring system therefore derives the pump position from the mechanical loading of the drive motor.

The mechanical loading of the drive motor can be ascertained in various ways in the context of the disclosure.

For example, the position measuring system can measure one or more electrical operating variables (e.g. operating current) of the electric drive motor by means of a drive controller and derive the mechanical loading therefrom. Thus the driving torque of an electric motor can as a rule be calculated from the operating current.

Another possible way of determining the mechanical loading of the drive motor consists in providing an additional torque transducer which measures the torque which acts on the drive shaft of the drive motor. For example, such a torque transducer may be a strain gauge, which is attached to the drive shaft of the drive motor or to a piston of the coating agent pump, the strain gauge measuring at the piston not the torque, but the force on the piston.

The above-mentioned two types of determination of the mechanical loading of the drive motor may be used on their own or in combination with each other. Furthermore, in the context of the disclosure other methods may also be used in order to ascertain the mechanical loading of the drive motor of the coating agent pump.

The position measuring system according to the disclosure permits accurate association of piston position with motor position, which permits very high dispensing accuracy. For example, the dispensing inaccuracy for a displaced volume of the pistons of 1600 cm³ may for example be less than 1 ml. The relative dispensing inaccuracy may therefore be less than 5‰, 2‰, 1‰ or 0.75‰, relative to the displaced volume of the piston pump.

Furthermore, it should be mentioned that the coating agent pump according to the disclosure preferably has a control unit which is connected on the input side to the position measuring system and on the output side to the electric drive motor. On the output side, the control unit actuates the electric drive motor. On the input side, the control unit receives the current value of the pump position from the position measuring system, which permits extremely accurate dispensing of the coating agent.

Feeding back the current pump position also makes it possible, in the case of a piston pump, for the piston speed to be specifically varied in order to reduce the disturbing pulsation of the conveyed stream of paint. The control unit therefore preferably controls the drive motor such that the piston when passing through its reversal points moves faster than between the reversal points. As a result, the disturbing pulsation of the coating agent pump can be reduced by a factor of 7 compared with a piston stroke of constant speed. This frequently makes it possible to dispense with the pulsation dampener in the fluid circuit which is otherwise necessary.

Furthermore, the coating agent pump according to the disclosure preferably has a pressure measurement means in order to measure the coating agent pressure at the exit from the coating agent pump. To this end, the pressure measurement means first of all ascertains the mechanical loading which acts on the drive motor from the coating agent pump. In particular, the pressure measurement means to this end may evaluate an electrical operating variable (e.g. operating current) of the electric drive motor. The pressure measurement means can then derive the coating agent pressure from the mechanical loading of the drive motor which is thus ascertained. This pressure measurement may under certain circumstances make it possible to dispense with additional pressure sensors. Furthermore, in this manner pressure fluctuations, which occur, for example, if coating agent is suddenly withdrawn at a tapping point, can be compensated more quickly. Measuring the coating agent pressure by measurement of the electrical operating variables at the drive motor is also considerably quicker than detecting external sensor signals by means of analog or digital converters, which makes more rapid reaction possible.

Further, the coating agent pump according to the disclosure may include a monitoring system in order to recognise a malfunction or wear of the coating agent pump. For example, the various measured variables, such as for example coating agent pressure, delivery rate and torque of the drive motor, are usually in a certain relationship to each other. If the actual measured values of coating agent pressure, delivery rate and torque then deviate from this stipulated relationship, this may indicate a malfunction or wear of the system. The monitoring system therefore ascertains during operation the relationships between measured variables of the pump points, the coating agent pressure, the mechanical loading of the drive motor and/or the delivery rate of the coating agent pump. If these relationships between the individual measured variables change over time, the monitoring system may then emit a warning signal, which may then also result in a corresponding automatic reaction. For example, this warning signal may be emitted to the control unit, which then terminates the pump operation.

Also temporally recurring fluctuations in torque can thus be used as a source of information for recognising faults of the system early on as well. For example, uneven wear of the deflection system, chips or soiling on the rail system or damaged teeth of the gear mechanism may be the cause of such a fault situation.

Also running dry of the coating agent pump, which results in very rapid wear of the seals of the coating agent pump, since these are lubricated by the paint, can be recognised if a speed of >0 opposes a very low torque or a very low force acting on the piston (then “only” air is pumped, which generates no back-pressure and hence no force).

Furthermore, the coating agent pump according to the disclosure may include a pressure limiter for limiting the pressure at the exit from the coating agent pump. The pressure limiter in this case preferably limits an electrical operating variable of the coating agent pump in order to prevent excessive pressure. The pressure limiter therefore limits the coating agent pressure in this case indirectly by limiting an electrical operating variable. In this case, the torque ascertained via the operating current or by means of strain gauges is limited and thus due to the relationship between pressure and torque/force the paint pressure is limited indirectly.

In one example of embodiment of the disclosure, the coating agent pump is a double-piston pump with two opposed pistons which are displaceable in one cylinder in each case. A double-piston pump of this type is known for example from U.S. Pat. No. 7,938,632 B2, the disclosure of which is expressly incorporated herein by reference. Preferably the pistons in this case are horizontally displaceable, while the drive motor has a vertically oriented drive shaft which runs between the two pistons. The drive motor in this case preferably acts on the two pistons via a rotatable cam disc. Furthermore, it should be mentioned that a planetary gear mechanism may be arranged between the drive motor and the cam disc. The drive motor and the electronics components in this case are preferably housed in an explosion-protected housing.

Some benefits of the disclosure are summarised as follows:

-   considerably reduced pulsation compared with comparable pump     systems, -   high-precision dispensing and high delivery rate possible with the     same pump, -   protection of the pump or seals from running dry, -   pressure control/monitoring without additional sensors, -   high efficiency and low energy consumption, in particular at low     speeds (if a synchronous servomotor is being used), -   preventive recognition of defects/wear, -   excess-pressure limitation without additional sensors, and -   automatic recognition of the piston position by recognition of     reversal points.

FIG. 1 shows a simplified schematic representation of a coating agent pump arrangement according to the disclosure with a double-piston pump 1 which is arranged in a coating agent line 2 and pumps paint through the coating agent line 2 in the direction of the arrow.

The double-piston pump 1 is driven by an electric drive motor 3, the drive motor 3 being electrically actuated by a control unit 4. The control unit 4 in this case stipulates electrical operating variables of the drive motor 3 and thereby also defines the torque with which the drive motor 3 drives the double-piston pump 1.

In this case, additionally a position measuring system 5 is provided which continuously detects the electrical operating variables of the drive motor 3 in order to ascertain the pump position therefrom. Thus pressure fluctuations occur at the reversal points of the pistons, as a result of which the forces acting on the pistons change. This change in forces then also has an effect on the drive shaft of the drive motor 3 and on the electrical operating variables of the drive motor 3. The position measuring system 5 can therefore ascertain the angular position of the drive shaft of the drive motor 3 and hence also the pump position by evaluating the electrical operating variables of the drive motor 3.

The position measuring system 5 then feeds back the current value of the pump position to the control unit 4, which makes it possible for the control unit 4 to actuate the drive motor 3 exactly, which permits very high dispensing accuracy.

Furthermore, the disclosure has a pressure measurement means 6 which likewise monitors the electrical operating variables of the drive motor 3 in order to derive the coating agent pressure downstream from the double-piston pump 1 therefrom. In this case, the fact that the correlation between torque and coating agent pressure and hence also the correlation between the measured electrical operating variables and the coating agent pressure is constant during operation, if changes due to wear are disregarded, is utilised. The pressure measurement means 6 then also feeds this pressure value back to the control unit 4, so that the control unit 4 can take into account the pressure value in actuating the drive motor 3.

Finally, a monitoring unit 7 which recognises a malfunction or excessive wear is additionally provided. In this case, the fact that the values of coating agent pressure, delivery rate and torque, and hence also of the electrical operating variables, occurring during operation are normally in a certain relationship to each other is utilised. If then a malfunction or excessive wear occurs, the relationship between these variables changes over the course of time. The monitoring unit 7 therefore detects the coating agent pressure and the pump position and checks whether the measured values are in a normal relationship to each other which indicates correct pump operation. Should this not be the case, the monitoring unit 7 assumes a malfunction or wear and transmits a warning signal to the control unit 4, which can then initiate suitable countermeasures.

FIGS. 2 to 4 show various views of a double-piston pump 8 according to the disclosure with an explosion-protected control panel 9, an explosion-protected drive train 10 and a lower fluid part 11.

In the explosion-protected drive train 10 there are a terminal box 12, a drive controller 13, a synchronous servomotor 14 with an integrated rotary encoder, and a planetary gear mechanism 15.

The angular position of the synchronous servomotor 14 in this case is therefore ascertained directly by the integrated rotary encoder.

On the upper side of the fluid part 11 there is first of all a coupling 16 which makes it possible to connect the explosion-protected drive train 10 to a cam disc 17. The cam disc 17 acts on slides 18 in the fluid part 11, the slides 18 in turn driving pistons 19. The paint to be conveyed is in this case supplied via a material inlet 20 and discharged via a material outlet 21.

The disclosure is not restricted to the preferred examples of embodiment described above. Rather, a large number of variants and modifications which likewise make use of the inventive concept and therefore fall within the extent of protection are possible. In particular, the disclosure also claims protection for the subject-matter and the features of the dependent claims independently of the claims referred to and in particular also without the features of the main claim. 

1.-16. (canceled)
 17. A coating agent pump for conveying a coating agent in a coating installation, having a) an electric drive motor for driving the coating agent pump so that the coating agent pump continuously changes its pump position during operation, and b) means for measuring a position and for quantitatively detecting the pump position of the coating agent pump.
 18. A coating agent pump according to claim 17, wherein the position measuring system is integrated in the coating agent pump.
 19. A coating agent pump according to claim 17, wherein the position measuring system is separated from the coating agent pump.
 20. A coating agent pump according to claim 17, wherein the position measuring system ascertains an absolute value of the pump position in contrast to an incremental value.
 21. A coating agent pump according to claim 17, wherein the position measuring system ascertains an incremental value of the pump position in contrast to an absolute value.
 22. A coating agent pump according to claim 17, wherein the drive motor is a synchronous motor.
 23. A coating agent pump according to claim 17, wherein the drive motor is an asynchronous motor.
 24. A coating agent pump according to claim 17, wherein the drive motor is a servomotor which has an integrated position sensor as part of the position measuring system in order to ascertain the position of the drive motor and hence also the pump position.
 25. A coating agent pump according to claim 17, wherein a position of a slide which is driven is measured.
 26. A coating agent pump according to claim 17, wherein a) the position measuring system ascertains the mechanical loading of the drive motor by the coating agent pump by means of a force or torque measurement means, and b) the position measuring system derives the pump position from the mechanical loading of the drive motor.
 27. A coating agent pump according to claim 26, wherein a) the position measuring system measures an electrical operating variable of the electric drive motor by means of a force or torque measurement means, and b) the position measuring system derives from the measured electrical operating variable the mechanical loading of the drive motor by the coating agent pump.
 28. A coating agent pump according to claim 26, wherein a) the force or torque measurement means has a torque transducer which measures a torque which acts on a drive shaft of the drive motor, and b) the torque transducer has a strain gauge which is attached to the drive shaft of the drive motor or to a piston of the coating agent pump.
 29. A coating agent pump according to claim 17, wherein the coating agent pump has an absolute dispensing inaccuracy of less than 50 ml relative to a swept volume of the piston pump of 1600 cm³.
 30. A coating agent pump according to claim 17, wherein the coating agent pump is a piston pump with a certain displaced volume, the coating agent pump having a relative dispensing inaccuracy of less than 5‰ relative to the displaced volume.
 31. A coating agent pump according to claim 17, wherein a) a control unit is provided which is connected on the input side to the position measuring system and on the output side to the electric drive motor, and b) the control unit actuates the electric drive motor as a function of the pump position ascertained by the position measuring system.
 32. A coating agent pump according to claim 31, wherein the control unit drives the drive motor in order to reduce pulsations of the delivery flow such that the piston when passing through its reversal regions moves faster than between the reversal regions.
 33. A coating agent pump according to claim 17, wherein a) a pressure measurement means is provided in order to measure the coating agent pressure at the exit from the coating agent pump, and b) the pressure measurement means ascertains the mechanical loading which acts on the drive motor from the coating agent pump, and c) the pressure measurement means derives the coating agent pressure from the mechanical loading of the drive motor.
 34. A coating agent pump according to claim 17, wherein a) a monitoring system is provided in order to recognise a malfunction or wear of the coating agent pump, and b) the monitoring system ascertains relationships between measured variables of the pump position, of the coating agent pressure, of the mechanical loading of the drive motor and/or of the delivery rate of the coating agent pump, and c) the monitoring system generates a warning signal in the event of a change in the relationships between the measured variables over time.
 35. A coating agent pump according to claim 17, wherein a) a pressure limiter is provided for limiting the pressure at the exit from the coating agent pump, and b) the pressure limiter limits an electrical operating variable of the coating agent pump in order to prevent excessive pressure.
 36. A coating agent pump according to claim 37, wherein: the coating agent pump is a double-piston pump with two opposed pistons which are displaceable in one cylinder in each case, and b) the pistons are horizontally displaceable and the drive motor has a vertical drive shaft between the two pistons, c) the drive motor drives the two pistons by means of a rotatable cam disc, and d) a planetary gear mechanism is arranged between the drive motor and the cam disc.
 37. A coating agent pump according to claim 37, wherein at least one of the drive motor and electronics components is housed in an explosion-protected housing. 